A cruise control system makes it possible to set the vehicle's speed to a desired level selected by the driver. If the sensor device for the vehicle incorporates a distance sensor, for example in the form of a radar sensor, a stereo camera system or the like, the vehicle speed can also be set in such a way that a suitable safety distance to a vehicle ahead is automatically maintained. The input device for the shut-off command, which may, for example, take the form of a control button on the steering wheel or dashboard, allows the driver to deactivate various control functions. Other operational commands from the driver, e.g., pressing the brake pedal, have the effect of deactivating the control functions.
An example of a cruise control system, which is also known as an ACC (Adaptive Cruise Control) system, is described in “Adaptive Cruise Control Systems—Aspects and Development Trends,” by Winner, Witte, Uhler and Lichtenberg, Robert Bosch GmbH, in SAE Technical Papers Series 961010, International Congress and Exposition, Detroit, Feb. 26–29, 1996. Since the available sensor devices do not yet permit complete coverage and safe evaluation of the traffic environment, at present such systems are primarily suitable for relatively stable traffic situations, such as driving on a highway or expressway. In urban traffic, or when driving at low speeds on winding roads, however, the uncertainties in detecting the particular relevant target object could create a risk of accident. For this reason, known ACC systems are designed in such a way that they can be activated only above a certain threshold speed.
Some systems attempt to expand the range of application of the ACC system to the traffic situation described as “stop-and-go,” which occurs, for example, in a traffic jam or in slow-moving traffic. This traffic situation, too, is relatively stable and is therefore suitable for automatic distance control. However, the functionality has to be expanded in such way that stopping and preferably also starting may be controlled automatically. On vehicles having automatic transmission, this may be achieved by means of accelerator and brake control signals, which have the same effect as the driver's pressing the accelerator pedal or brake pedal. However, it must be ensured that road safety is not jeopardized by vehicle responses which the driver is not expecting.
An object of the present invention is to provide a cruise control system which makes it possible to automatically brake the vehicle to a standstill and to hold the vehicle in stationary position without jeopardizing road safety.